diff --git a/src/libsyntax/ast.rs b/src/libsyntax/ast.rs
index c7ebc344a9c8..8a9bd5192ad8 100644
--- a/src/libsyntax/ast.rs
+++ b/src/libsyntax/ast.rs
@@ -24,7 +24,7 @@ use extra::serialize::{Encodable, Decodable, Encoder, Decoder};
 // table) and a SyntaxContext to track renaming and
 // macro expansion per Flatt et al., "Macros
 // That Work Together"
-#[deriving(Clone, Eq, IterBytes, ToStr)]
+#[deriving(Clone, IterBytes, ToStr)]
 pub struct Ident { name: Name, ctxt: SyntaxContext }
 
 impl Ident {
@@ -32,6 +32,19 @@ impl Ident {
     pub fn new(name: Name) -> Ident { Ident {name: name, ctxt: EMPTY_CTXT}}
 }
 
+impl Eq for Ident {
+    fn eq(&self, other: &Ident) -> bool {
+        if (self.ctxt == other.ctxt) {
+            self.name == other.name
+        } else {
+            fail!(fmt!("not allowed to compare these idents: %?, %?", self, other));
+        }
+    }
+    fn ne(&self, other: &Ident) -> bool {
+        ! self.eq(other)
+    }
+}
+
 /// A SyntaxContext represents a chain of macro-expandings
 /// and renamings. Each macro expansion corresponds to
 /// a fresh uint